1. Field of Invention
The present invention relates to a backlight module. More particularly, the present invention relates to a light-emitting diodes (LED) backlight module that can reduce dark stripes.
2. Description of Related Art
A backlight module is one of the fundamental parts in a liquid crystal display (LCD). Since liquid crystal does not emit light itself, the backlight module is needed for providing the required light source. The principle for operating a backlight module is to direct the light emitted from a backlight source as a planar light source via a light guide plate, thereby assuring uniform brightness. A backlight source commonly used in the backlight module can be a cold cathode fluorescent lamp (CCFL) and an LED, etc. Although the CCFL is the main trend currently, yet the demands for using the LED as the backlight source have been increasing daily. In comparison with the CCFL used as the backlight source, the LED has the advantages of small size, long operation life, low driving voltage, low power consumption and excellent shock resistance, etc.
The LED is a point light source, and thus the shadow display of dark stripes appears between two adjacent LEDs applied in an LED backlight module, due to the size and arrangement of the backlight module; and the light-emitting surfaces of the LEDs which are too close to an active area of the light guide plate. Referring to FIG. 1, FIG. 1 is a schematic diagram illustrating dark stripes shown on a conventional LCD. The conventional LCD comprises a rectangle frame 102 having four connected sides; and an LED 10 and an LED 12 mounted on one of the four connected sides of the rectangle frame 102. There is a distance between the LED 10 and LED 12, and the LED 10 and LED 12 have a light scattering angle A1 and a light scattering angle A2 respectively, wherein the light scattering angle A1 and A2 are generally between 90 degrees and 110 degrees. Such as shown in FIG. 1, when the LEDs 10 and 12 are very close to the active area of the LCD, dark-stripe regions 30 are clearly shown between the LEDs 10 and 12; and between the LEDs 10 and 20 and the rectangle frame 102. Although the dark-stripe regions 30 can be reduced by increasing the distance between the active area and the LEDs 10 and 20, yet the increased distance would reduce the intensity of the light emitted onto the active area from the LEDs 10 and 20, so that the LEDs have to be applied with bigger power to prevent light intensity reduction. Besides, when the distance between the active area and the LEDs 10 and 20 is increased, a light guide plate with larger area has to be used, thus not only causing the increase of production cost but also failing to effectively utilize the limited space in the backlight module.